Hand held spray dispensers are typically either of the manually-actuated spray pump type or the aerosol spray type. Aerosol spray dispensers utilize a liquefied gas propellant that “flashes off”, to create a fine spray. These ultra fine sprays have mean droplet diameters on the order of about 40 microns. Such a spray characteristic is desirable in many applications in cosmetics and industrial coatings. This sprayer however has several disadvantages. The composition contains a large volume of liquefied gas and other volatile organic compounds (VOCs) which are known to react with certain nitrogenic oxides (NOx), which in turn may result in the formation of ground-level ozone—a potential source of health problems. Certain propellants such as hydrocarbons and hydro-fluorocarbons gases also contribute to global warming. Therefore, there are ecological pressures to reduce, or avoid entirely, the use of VOCs in aerosol products.
Manually-actuated spray pump dispensers or finger pumps rely on the consumer to generate a hydraulic pressure in the pumping engine in order to dispense the fluid. Most pumping engines typically use a standard piston and cylinder arrangement to generate hydraulic pressure. When the consumer applies an actuation force by pushing downward on the piston, the hydraulic pressure of the fluid in the cylinder is increased. Most manually-actuated spray pump dispensers have been unable to produce sprays having a mean droplet diameter of less than about 55 microns. These larger mean particle sizes, produced by conventional manual spray pumps is too coarse for many applications. These larger particle sizes result in sprays that users refer to as “wet”.
Most conventional spray pumps operate at a hydraulic pressure of about 6 bar. Research has indicated that when the hydraulic pressure in these conventional spray pumps is increased upward to levels near about 14 bar, mean droplet diameters of about 40 microns or less are achievable.
A method of developing a high hydraulic pressure of about 14 bar requires actuation force from about 44 Newton to about 88 Newton. An actuation forces in this range is too excessive for most consumers to attain by manual pumping. Such an actuation force can quickly fatigue the finger and hand of even the most physically adept person, let alone the typical users of most finger pumps.
A need exists for an aerosol propellant method that is capable of delivering substantially higher hydraulic pressures to create a fine spray driven by aerosol created pressure while reducing the ecological problems associated with existing aerosol propellant dispensers.
The present invention provides a new dispensing device and dispensing method that produces 14 bar of pressure for dispensing liquid in a fine spray. The device comprises a spring-loaded piston member and valve system similar to that in a finger-triggered spray pump. The activation force however is generated by the expansion of liquefied gas stored in a small gas compartment within the pump. The piston is configured to multiply the gas pressure and transmit higher pressure to the fluid composition in the nozzle. It has been found that the amount of liquefied gas that is needed is about 1/10th when compared to propellant-based aerosol that produces the same aerosol characteristics.